A hinge generally comprises two elements articulated to one another, one of which comprises at least one fork supporting the hinge pin and the other comprises at least one hub mounted on the pin supported by the fork, each bearing of the fork and each hub being connected by a tenon to a leaf of the hinge.
In this type of hinge, provision is rarely made to provide, at the maximum opening angle, elasticity other than that inherent in the component material of the element connected with one of the elements of the hinge, such as the temple when an eyeglass temple is involved.
In addition, provision is rarely made, not only in hinges designed for hinging the temples of eyeglasses, but also in those intended for other articulations like those of automobile doors or the doors of furniture, more especially kitchen furniture, of means tending to hold elastically the two elements of the hinge in a closed position, in other words, in the position corresponding to the minimum angle. These means are generally composed of a plunger in the form of a ball accommodated in a recess in one of the elements of the hinge and continuously urged by a spring against a cam-shaped section provided in the other element of this hinge.
It will be readily understood that means of this kind have a high cost by virtue of their design and the operations required to install them, and their cost also increases inversely with the size of their component parts, which is clearly the case when hinges for eyeglasses temples are involved.